1. Field of the Invention
The present invention relates to a gas valve assembly, and more particularly, to a permeable gas valve assembly that controls fluid flow from a fluid source to a processing tool.
2. Description of the Related Art
Many industrial processing and manufacturing applications require the use of highly toxic fluids. The manufacture of semiconductor materials represents one such application wherein the safe storage and handling of highly toxic hydridic or halidic gases becomes necessary. Examples of such gases include silane, germane, ammonia, phosphine, arsine, stibine, hydrogen sulfide, hydrogen selenide, hydrogen telluride, and other halide compounds. As a result of toxicity and safety considerations, these gases must be carefully stored and handled in the industrial process facility. The semiconductor industry in particular relies on the gaseous hydrides of arsine (AsH3) and phosphine (PH3) as sources of arsenic (As) and phosphorus (P) in ion implantation. Ion implantation systems typically use dilute mixtures of AsH3 and PH3 at pressures as high as 1500 psig. Due to their extreme toxicity and high vapor pressure, their use, transportation and storage raise significant safety concerns for the semiconductor industry.
For example, arsine is an extremely toxic gas that is used by the semiconductor industry and typically stored in pressurized containers at about 250 psi. The handling of arsine cylinders in production environments presents a wide variety of hazardous situations. A leak in one 140 gram cylinder of arsine could contaminate the entire volume of a 30,000 square foot building with 10 foot high ceilings to the Immediate Danger to Life and Health (IDLH) level. If the leak were large, such contamination could occur in a few minutes, which would mean that for many hours there would be extremely deadly concentrations in the area near the source of the spill.
Gas pressure regulating valves of the type for delivering gas at a relatively low pressure, have been known and used for many years. However, these valves are subject to leakages of the highly pressurized gas along valve stems. Unless some provision is made for preventing such leakage, the build-up of high pressure gas leakage in trapped volumes within the valve device can introduce an unintended bias into the regulator and produce distortion of the delivery control. In order to nullify the effect of leakage, some pressure regulating valves resort to the use of a constantly open atmospheric vent port for releasing gas leakage directly to the atmosphere. Clearly, in the case of inflammatory gas or explosive gases the possible accumulation of released gas in a confined area becomes a serious health and safety hazard, and an open port is not an option.
In view of the serious potential for injury or death that could result from an unintended release of these fluids, the prior art discloses systems for preventing such catastrophic release of toxic fluids. U.S. Pat. Nos. 5,704,965; 5,704,967; 5,707,424; and 5,518,528 teach systems for storage and dispensing of gases, e.g., hydridic and halidic gases, which operate at ambient temperature by using a pressure reduction to desorb toxic fluids from zeolite, carbon, or other adsorbent materials having high storage (sorptive) capacity for these gases. In these systems, gas is adsorbed and stored on the physical adsorbent in a fluid storage and dispensing vessel and is desorbed from the adsorbent and discharged from the vessel under dispensing conditions. In such systems, the gas can be stored and dispensed at sub-atmospheric pressure levels, typically below about 700 torr. Physical adsorbent-based systems of such type are commercially available from ATMI, Inc. (Danbury, Conn.) under the trademarks SDS and SAGE.
One issue associated with such adsorbent-based fluid storage and dispensing systems relates to the maintenance of high purity of the dispensed gas, since the purity of the gas is reduced if residual absorbent material that is entrained in the discharging gas.
The development of the above-described adsorbent-based fluid storage and dispensing systems has been motivated by safety and reliability issues involving packages of high-pressure gases in the semiconductor industry, as part of efforts in recent years to significantly increase the safety of gas packaging.
Another recent development in the field of enhanced safety fluid storage and dispensing systems is the evolution of systems in which fluid is contained in a vessel having a fluid pressure regulator in the interior volume of the vessel. Such arrangement permits fluid to be stored at high pressures, with the regulator being operative to discharge fluid from the vessel only when it sees a downstream pressure that is below the set point of the regulator. Such internally disposed regulator systems are more fully described in U.S. Pat. Nos. 6,101,816 and 6,089,027, and are commercially available from ATMI, Inc. (Danbury, Conn.) under the trademark VAC.
Despite these developments of safer gas packaging, it remains critical for gas packages to be fabricated without the occurrence of, or potential for, fluid leakage, and to minimize adverse effects that may result from valve mishandling or valve failure in the use of such gas packages.
Accordingly, there is a need in the art for a fluid delivery system that avoids the occurrence of releases of highly pressurized toxic fluid to the ambient environment of the system, or impairment of the purity of the discharged fluid due to the presence of entrained absorbent material therein.
It would therefore be a significant advance in the art to provide a fluid delivery system that reduces the possibility of accidental spillage or release of toxic liquid or gases, eliminates the need for sorbents to control the handling, storage and delivery of toxic fluids, and constrains the flow of fluid during normal operation as well as during any kind of valve mishandling or valve failure.